1. Technical Field
This invention relates generally to gas turbine engines and particularly to an arrangement for mounting a rotatable component on the rotor of such a gas turbine engine.
2. Background Information
Gas turbine engines, such as those which power aircraft, employ a stator which supports stationary components of the engine, such as vanes which direct the flow of air and combustion gases through the engine, and a rotor of the stator on which rotatable components such as fan, compressor and turbine blades are mounted. Such blades are ordinarily mounted on hubs therefore which are fixed to one or more rotor shafts which extend through the interior of the stator. It is a common practice to mount such hubs on mounting flanges or bases which are either fixed to the rotor shaft or integrally formed therewith. Such hubs are typically fixed to the associated mounting flanges or bases in arrangements wherein elongate fasteners such as bolts extend through overlying apertures in the hubs and associated mounting flanges. Consistent with known manufacturing techniques, it is a common practice to provide the mounting holes in the hubs and flanges that are slightly larger than the cross-sectional areas of the bolts which extend therethrough to allow the bolts to be inserted in the apertures without binding thereon. This arrangement defines a clearance between the bolts and the mounting apertures. Under operating conditions such as surge events wherein the engine rotor experiences a radial imbalance of working fluid flow, the presence of such clearances between the bolts and mounting apertures allow a radial shift of the hub on the mounting flange, inducing a radial imbalance in the rotor, resulting in whirl which can damage the rotor by a bending of the shaft or a mechanical failure of the bearings on which the shaft is mounted. Accordingly, it is imperative that such radial imbalances in the rotor be avoided as much as possible. One known method for avoiding such radial imbalances caused by a shifting of the hub on the mounting flange is to entirely eliminate the clearances between the mounting bolts in the apertures and the hub and flange through which the bolts extend. Such clearances may be eliminated by forming the apertures with precisely the same area as the bolt shanks. However, such arrangements add substantially to engine rotor engine rotor manufacturing efforts quality control problems and therefore costs, requiring extreme precision in the formation of the mounting apertures and difficulty in insertion of the bolts into such apertures due to the bolts binding on the interior surfaces of the apertures when inserted therethrough.
Accordingly, an arrangement for mounting a rotatable component on a gas turbine engine rotor which minimizes the risk of any radial imbalance of the rotor due to radial shifting of the component on a mounting flange or base therefor without requiring excessive precision in the formation of mounting apertures and increase costs associated with the assembly of such a mounting arrangement due to a lack of clearance between the mounting bolts and the apertures within which such bolts are received, is sought.